    var $lis = $("li");
    var arr = ["1.png","2.png","3.png","4.png","5.png","6.png"];
    var $input = $("input");
    var during = 5000;
    var degrees = 0;
 
     $lis.each(function (i) {
          
          var url = "url(" + arr[i] + ")";
          $(this).css("background",url);
          //$(this).css("background-size","400px 200px"); 
         })
          $("ul li:lt(4)").each(function (i) {
            $(this).css("background-size","400px 200px"); 
         })
          $("ul li:gt(3)").each(function (i) {
            $(this).css("background-size","200px 200px"); 
         })
    
 
     
   
  $input.click(function () {     
          degrees -= 90
          $("#flat").css("transform","rotateX("+degrees+"deg)");
          $("#flat").css("transition-duration","3s");
      })

